A diagonally connected MHD generator channel or duct is one of the most preferred types of channels or ducts employed within MHD electric power generators due, for example, to the simplicity of the electrical connections between the generator electrodes and the external power system. A typical diagonal type MHD power generator channel or duct comprises an axially stacked assembly of a large number of individual, annular, rectangular forms or frame elements, commonly referred to as "window frames", which are electrically isolated or insulated from one another and cooled by means of a liquid passing through coolant channels operatively associated with each frame element. Exemplary diagonal type window frame MHD generators are disclosed within U.S. Pat. Nos. 3,940,640, 3,940,639, and 3,148,291, it being noted that the coolant channels are not disclosed.
Construction of diagonal type MHD generators is rendered difficult in view of the fact that the planes of the frame elements are inclined relative to the generator channel's longitudinal axis, as indicated within the aforenoted patents by the angle .theta., wherein .theta. is less than 90.degree. and is commonly 45.degree.. This difficulty is enhanced further by the fact that the angle of inclination of the frame elements varies within the end regions of the channel in order to accommodate the varying inclination of the equipotential lines that characterize these channel end regions. This requisite inter-frame angular variation is resolved by costly and complex means, such as, for example, the fabrication of window frame elements exhibiting tapered thickness dimensions as viewed along their diagonal components. Additional fabrication difficulties are also presented in view of the fact that internal coolant passages must be defined throughout the entire annular extent of the frame elements.
The aforenoted features of diagonal type MHD generator channels thus render the fabrication thereof quite costly, as will become even more apparent hereinbelow, particularly when adherence to predetermined quality control standards is to be achieved. For example, as can readily be seen from the foregoing discussion, the generator duct or channel must meet particular geometrical requirements, as must the contour characteristics of the coolant passages. Dimensional consistency is likewise required to be maintained in connection with the interframe mating surfaces, and the assembled integrity of the generator channel must be assured in order to maintain the fixed disposition of the frame element insulators, the overall structural stability of the channel, and the satisfactory performance of the cooling system.
In the fabrication of conventional diagonal type MHD generator channel frames, there exist basically two different methods of construction. In accordance with a first method of constructing such frames, the same are machined from solid plate material. The ability to precisely control the machining processes facilitates the accurate production of geometrically complex structures with a high degree of manufacturing predictability and reliability, and thus, this method is particularly useful for channel frame construction, especially in connection with the fabrication of the end frame elements having variable plate thicknesses. The method, however, involves substantial fabrication expenditures, and is severely limited in connection with the production of particularly contoured coolant passages within the frame elements. In accordance with this method, for example, a continuous groove must be machined throughout the entire annular extent of each frame element either within an edge or side surface thereof, not unlike that shown, for example, within U.S. Pat. No. 3,374,368, although it is seen that the frame element of such patent is not fabricated from a single component of plate stock. Nevertheless, whether the entire frame is to be fabricated from a single component of plate stock, or from individual frame members joined together, the machining processes required for forming the coolant grooves or passages necessitate the removal of substantial amounts of the plate material. In addition, as can readily be appreciated from U.S. Pat. No. 3,374,368, particularly FIGS. 9 and 10 thereof, in view of the fact that the coolant passage is machined within one surface of the plate and is thus closed upon three sides thereof yet open along one side thereof, that is, the machined side, in order to define a completely enclosed coolant passage, specially designed cover plates or caps are required. Such components of course involve additional material expenditures and assembly time. The cap members or cover plates are conventionally welded to the frame elements, and additional machining is often required within the weld regions subsequent to the completion of the welding operations. While this first method would be substantially simplified if a circular, rather than a particularly contoured, coolant passage profile was defined within the frame elements, since such profiles could simply be generated by conventional gun-drilling techniques, circular coolant passages have been unacceptable in that the same do not exhibit satisfactory heat transfer or heat exchange properties, especially in connection with the MHD electrodes.
The second conventional method of constructing diagonal type MHD generator channel frames is achieved by bending either a straight solid bar, a straight open-sided bar of the type discussed hereinabove in connection with U.S. Pat. No. 3,374,368, or a straight hollow bar, into the required framework element and welding the ends together so as to form the annular component. In accordance with this method, wherein the bar stock has, for example, a rectangular cross-sectional profile, machining of the channel or duct bore is of course entirely obviated as the bar is bent so as to conform to the appropriately required bore geometry and dimensions as determined by the inner periphery of the bar annulus. However, as the frame element is to be disposed within a diagonal plane, the electrode portions of the frame element must necessarily have a cross-sectional profile corresponding to that of a parallelogram. Consequently, a considerable amount of bar stock material must be removed by machining processing from the interior or bore and exterior regions of the frame electrode portions subsequent to the welding together of the bar ends. In addition, an extensive amount of material must also be removed from the bar stock in order to provide or define the coolant passages as in the case of machining the frame elements from plate stock.
When open-sided bar stock, having, for example, a rectangular cross-sectional profile, is utilized in accordance with this second method, the machining processing required for defining the coolant passages within the diagonal portions of the frame elements is of course eliminated, however, as noted in conjunction with the structures of U.S. Pat. No. 3,374,368, cover plates or cap members will be required. In addition, machining of the electrode portions of the frame elements will be required in order to convert the cross-sectional profile thereof to that of a parallelogram. Similarly, some machining will likewise be required in order to convert the coolant passage profile within the electrode portions of the elements from that of a rectangle to that of a parallelogram such that the contours of the coolant passages match those of the electrode frame portions per se.
Lastly, if hollow bar stock, having, for example, an exterior rectangular cross-sectional profile and an interior bore having, for example, a cross-sectional profile simulating a parallelogram, were utilized for forming the frame elements of the MHD generator channel, similar machining and unacceptable standards problems would likewise be presented. The electrode portions of the frame elements would have to be machined as in the previous two instances of solid and open-sided bar stock in order to convert the rectangular bar stock into parallelogram-profiled stock, however, it would be noted that the diagonal members of the frame elements, which have an exterior rectangular cross-sectional profile, have contoured coolant passages the cross-sectional profiles of which are those of parallelograms. Since these profiles do not match those of the bar stock per se, unacceptably poor heat transfer or heat exchange properties would characterize these frame element members.